I took the official NPC Grian skin file and updated the arm textures to the version in the videos. Due to NPC Grian not being a player, but instead an in-game model, some of the textures seen in the video are oddly stretched. An example would be the bottom and top of the arm; so I tried to replicate the look on this skin's arms. However, in the video the pant's texture is also very odd due to them being much thinner, and so, I don't think that it's possible to recreation it perfectly.

I also removed the 2 extra torso arms, which were no different than the left and right arm textures.

Edit: Apparently, the side hair textures (waffles) weren't video accurate either, so I fixed that.

Credit to Bugaboo8 for finding the original NPC Grian skin file.